Meteor Wayne nailed it while I was looking around.
That picture is a composite image from several telescopes. The red is from Chandra, the "white" from Hubble and Magellan, the blue is a computed mass distribution deduced from gravitational lensing and not really a "picture" at all. Since most of the mass (blue) isn't where the light (red/white) comes from they interpret it as evidence for the existence of dark matter.
The streak really got me going and I looked around a lot. The best spots I found are here:
http://chandra.harvard.edu/photo/2006/1e0657/more.html
http://chandra.harvard.edu/photo/2006/1e0657/media/
The first has links to almost all the separate parts of the picture. I say almost because I haven't been able to find separate pictures from the Hubble and Magellan observatories, my guess was the streak is only in one of them, but now I think both. The second has a links to several .pdfs that tell how they made the picture and has the Magellan part but it is very low res. The X-ray part doesn't have the streak but the optical part does. In the optical picture it is very faint. As they layer on the Chandra and computed parts the pixels add up and get brighter and brighter.
My initial guess was that it is a comet, asteroid or maybe Oort cloud object because it looked thin to be from gravitational lensing. Well, I'm glad I looked before I typed because page 14 of the last .pdf has pictures of your arc and more! I now think it is gravitational lensing of a background galaxy and part of what they used to compute the blue part of your original picture.
Here's a link to
A Direct Empirical Proof of the Existence of Dark Matter .
http://chandra.harvard.edu/photo/2006/1 ... /paper.pdf
The .pdf with the arc.
http://arxiv.org/pdf/astro-ph/0608408v1.pdf